This invention relates to a metallized plastic film electric capacitor incorporating a safeguarding device against explosion.
As is known, metallized plastic film capacitors, in time, undergo progressive deterioration of their electric characteristics due to instantaneous over-voltages causing perforation of the dielectric, or to ageing of the dielectric, or other causes. When such causes make the regenerative ability of the capacitor ineffective, an irreversible deterioration process begins, accompanied by the development of gas and a considerable increase in internal pressure, which may result in the capacitor exploding, with consequent serious damage for any surrounding equipment and danger for any persons in the proximate vicinity.
Furthermore, it may happen that rupture of the capacitor, by admitting air oxygen thereinto, triggers a combustion process leading to obviously serious situations.
In an attempt to obviate such drawbacks, capacitor designs have already been proposed, wherein the outer case is formed as a metal shell pleated with annular corrugations to thereby allow the shell to expand axially in the event of an excessive increase of the capacitor internal pressure.
That expansion is utilized to place under tension, and accordingly break, at least one of the two leads connected to the capacitor plates, thus cutting off the current supply and stopping the development of gas.
However, conventional capacitors have not negligible disadvantages which mainly originate from the complexity of the shell construction and effectuation of the connections.